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<h1>Runtime Library Support</h1>GWT supports only a small subset of the classes available in the Java 2
 Standard and Enterprise Edition libraries, as these libraries are quite
 large and rely on functionality that is unavailable within web
 browsers. To find out exactly which classes and methods are supported
 for core Java runtime packages, see the API reference for
 <code><a xmlns="" href="java.lang.html">java.lang</a></code> and
 <code><a href="java.util.html">java.util</a></code>, which lists supported
 classes and contains notes on behavioral differences from the standard
 Java runtime.
 
 <p>
 Some specific areas in which GWT emulation differs from the standard
 Java runtime:
 <ul class="featurelist">
<li>
<div class="heading">Regular Expressions</div>
<div> The syntax
 of <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html">Java
 regular expressions</a> is similar, but not identical, to <a href="http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Guide:Regular_Expressions">JavaScript
 regular expressions</a>. For example, the
 <a href="java.lang.String.html#replaceAll(java.lang.String, java.lang.String)">replaceAll</a>
 and <a href="java.lang.String.html#split(java.lang.String)">split</a> methods use regular
 expressions. So, you'll probably want to be careful to only use Java
 regular expressions that have the same meaning in JavaScript.</div>
</li>
<li>
<div class="heading">Serialization</div>
<div>Java serialization
 relies on a few mechanisms that are not available in compiled
 JavaScript, such as dynamic class loading and reflection. As a result,
 GWT does not support standard Java serialization. Instead, GWT has an
 <a href="com.google.gwt.doc.DeveloperGuide.RemoteProcedureCalls.html">RPC</a> facility that provides
 automatic object serialization to and from the server for the purpose
 of invoking remote methods. </div>
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<div class="tipCallout">Tip</div>
<div class="tipBody">You'll save yourself a lot of frustration if you make sure that
      you use only translatable classes in your
      <a xmlns="" href="com.google.gwt.doc.DeveloperGuide.Fundamentals.ClientSide.html">client-side code</a>
      from the very beginning. To help you identify problems early, your
      code is checked against the JRE emulation library whenever you run
      in <a href="com.google.gwt.doc.DeveloperGuide.Fundamentals.HostedMode.html">hosted mode</a>. As
      a result, most uses of unsupported libraries will be caught the
      first time you attempt to run your application. So, <i>run early
      and often</i>.</div>
</div>
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<h2>Related topics</h2>
<a xmlns="" href="java.lang.html">java.lang</a>,<a href="java.util.html">java.util</a>
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